Follow focus devices allow the constant and precise adjustment of the focus, which is indispensable for the definition of the image when the distance of the camera to the object to be photographed changes during an exposure.
The use of such a follow focus makes it possible for the camera assistant responsible for image definition to easily rotate the focus adjustment ring without having to directly take hold of the lens.
Existing follow focus devices, such as those known, for example, from CA 26 63 343 A1 or DE 94 15 170 U1, comprise a bevel gear with which the rotation generated by the camera assistant is transmitted via intermeshing gear wheels from a first axis to a second axis. However, such gear wheels comprise a certain backlash, and therefore with manual rotation, particularly when the direction of rotation is changed, the backlash must first of all be overcome. In order to minimize this backlash, the gear wheels are often produced with a high degree of precision and low tolerances. This results in high costs of production. Moreover, even with precision manufacturing it is not possible to completely eliminate the backlash. Yet even a small degree of backlash can disturb or distract the camera assistant from his work. The work of a camera assistant has to be carried out with a high level of concentration and backlash results in the operation of the mechanism feeling imprecise. This occurs particularly in the case of slow focus operations and changes in the direction of rotation.
In order to counter this negative feeling, grease dampers were provided in the state of the art, which were supposed to convey the feeling to the camera assistant that there was no backlash. However, these systems did not overcome the disadvantage that the rotation by the camera assistant did not immediately lead to a rotation of the focus adjustment ring but only after the backlash had been overcome.